This invention relates generally to a twin rotor disc brake primarily, but not exclusively, for heavy commercial vehicles.
Disc brakes include a rotor having opposite annular faces to which brake pads are applied by a caliper. Hydraulic actuation is generally provided in passenger and light commercial vehicles, and the brake pads are applied to the rotor by opposed pistons of the caliper, or by a single piston caliper having a sliding yoke. Heavy commercial vehicles rely upon air actuation, which necessarily requires a relatively large air actuator.
Disc brakes are preferred over drum brakes because of their increased performance and ease of inspection and maintenance. However, a rotor diameter is generally restricted by a vehicle wheel diameter, and in some cases a swept area of the rotor may be insufficient for the weight of the vehicle. Accordingly, twin rotor disc brakes have been developed, but in order to use a single caliper, one or both of the rotors must slide axially relative to the axle, for example on splines. This arrangement is not wholly satisfactory because sliding splines are relatively expensive to manufacture and have a tendency to stick due to corrosion or an accumulation of dirt and brake pad residues. Multiple calipers are not practicable. It would be desirable to provide a single caliper, twin rotor disc brake in which the rotors are relatively fixed, but the caliper has a single actuator.
A further problem of twin rotor disc brakes is that they are generally mounted at axle ends, and in use at least partially shrouded by the wheel. Accordingly, removal of the wheel is necessary for inspection and replacement of the brake pads and/or the rotors. Frequently brake pad wear is uneven so that semi-worn brake pads are replaced at the same time as fully worn pads in order to avoid an intermediate inspection. It would be desirable to equalize brake pad wear and to provide a way of actuation suitable for mid-axle location, where appropriate. Such an arrangement would be especially useful in undriven rigid axles of e.g., semi-trailers, so that unnecessary wheel removal is avoided. Generally speaking, wheel removal should be avoided if possible because of the well known problem of settling of freshly tightened wheel nuts, which can lead to loosening of the nuts and wheel shedding.